The invention relates to spherical metal support catalysts, a process for their production, and a process for the hydrogenation of aromatic substances.
In the use of catalysts in fixed-bed reactors, the spherical form of the catalysts leads to a uniform packing of the catalyst bed and thereby to the avoidance of undesired channels.
The production of spherical catalysts is sufficiently described in the literature. Numerous examples for the production of oxidic substrates by the application of the dropping of hydrosols into various solutions are protected: U.S. Pat. No. 4,198,318 describes the production of spherical Al2O3 substrates by the dropping of an acidic hydrosol into an aqueous ammonia solution in the presence of a non-ionic surface-active agent. In DE 403 5089 the dropping is accomplished by a vibrating nozzle plate. US 2001/0012816 A1 describes the dropping of mixtures of polysaccharide solutions with hydrated Al2O3, SiO2 Al2O3, ZrO2 Al2O3, or TiO2 Al2O3 gels or with Al2O3, B2O3 Al2O3 or B2O3 SiO2 Al2O3 hydrates in an aqueous solution of Ca2+, Al3+, Mg2+, Ba2+ or Sr2+ ions.
All dropping processes described previously are, however, based solely upon oxidic substrates. Dropping processes for the production of metal support catalysts with a metal content>10% by mass, which must be reduced after the dropping, drying, and possible calcination, have not been described previously.
A further method for the production of spherical catalysts is the granulation process, which however does not lead to a uniform spherical size. Further disadvantages of this process are the rough surface of the spheres as well as the irregular distribution of pore sizes over the cross-section of the sphere.
Furthermore, spherical catalysts are made with the use of “spheronizers.” Therein, formed pieces already produced are formed into spheres on a rotating plate, as, for example, is described for oxidic substrates in WO 99/58236. In these processes, the porosity is pre-determined in large part in the forming into extrudates, and the uniformity of the spherical size and the spherical shape is, moreover, unsatisfactory.